A dinosaur with "mummified" flesh has been unearthed in the United States, giving scientists an unprecedented insight into the soft tissues that are almost always lost during the fossilisation of these large animals.

British researchers involved in the project said yesterday that the near-perfect preservation of the plant-eating dinosaur's skin has enabled them to build up an exceptional picture of the animal, including the ability to estimate its top speed of 28mph.

This means that the duck-billed dinosaur, belonging to a group called the hadrosaurs, could out run the top predator, Tyrannosaurus rex, which shared the same terrestrial habitat as the hadrosaurs 67 million years ago.

The dinosaur was first discovered in 1999 by a budding scientist called Tyler Lyson, who was then just 16, on his family's land in North Dakota, but it is only in the past year or so that scientists have realised its significance.

Phillip Manning of Manchester University, who has worked alongside Mr Tyler, who is now at Yale University, to investigate the fossil, said that it is unusual to have a dinosaur specimen with such a large segment of intact skin, especially since the skin has not been flattened in fossilisation.

"It is quite fair to say that our dinosaur mummy makes other dinosaurs look like road kill. Simply because the evidence we're getting from our creature is so complete compared to the disjointed sort of skeletons that we usually have to draw conclusions from," Dr Manning said. "It lived in a flood plain so it really is unique for the skin to survive. Plant-eating dinosaurs have a reputation for being pretty boring but this find changes all that."

"Here, for instance, we can use the skin to estimate the size of the muscles it must have enveloped, and this can be done on this specimen more so than any other dinosaur in history."

The rock containing the fossilised remains has been carefully excavated and then subjected to a detailed internal analysis by a giant CT scanner operated by the Boeing aircraft company, which it normally uses to test spacecraft parts for Nasa.

Dr Manning said one of the most important revelations was that the rear end of the dinosaur appears to have been about 25 per cent larger than was previously thought. This would have enabled the dinosaur to reach top speeds of 28 mph.

The analysis has also found evidence that the hadrosaur had coloured stripes on its skin, possibly for camouflage. Although colour pigments do not fossilise, scales on the skin show that they are banded in size, which is often seen in present-day lizards that have striped markings based on scale size.

It is not known why the skin of this specimen has been preserved so well, but it must be because the mineralisation of the soft tissues took place at a faster rate than bacterial decay, Dr Manning said.

The UK premier of the documentary Dino Autopsy is shown this Sunday at 9pm on the National Geographic Channel.